This invention pertains generally to steam generator secondary piping systems, and more particularly to such systems as are shared, in part, among a plurality of steam generators.
Nuclear steam generation systems commonly employ a plurality of steam generators which communicate steam to a common header to drive a single turbine, and in turn, receive feedwater from a common condensate reservoir. Presently, in a number of plants, a secondary line break is detected by monitoring the respective steam exit pressures of the several generators in the system and the corresponding feedwater flow rates. Upon a feedwater line break at the inlet to any of the generators the pressure in the remaining steam generators will similarly drop due to the mutual coupling of steam lines of the several generators at the common header. However, the flow rate to the generators having feedwater lines that remain intact will decrease, while the flow rate through the broken line will increase. Although pressure is monitored in this arrangement the flow rate is employed to identify the line break.
A change in the operation action requirements specified by governmental regulations necessitates that either corrective action for a break be implemented automatically or flow restrictors be employed in the feedwater lines. Flow restrictors are undesirable because they increase the pump capacity required during normal operation. Automation of present procedures employed to correct feedwater line breaks would apply the flow rate signals as a means for implementing the corrective action previously established manually. However, an automated system responsive to the flow rate signals would be highly susceptible to unnecessary reactor trips since the flow rate setpoints would have to be flexibly adjusted to accommodate start-up, shut-down and normal power operation variations.
Accordingly, a new feedwater alignment system is desired that will function to take corrective action in the event of a secondary line break without causing spurious trips.